Need documentation for Leadership Change

### Describe the issue

The currently Leadership Change checklist for SIGs is 15 items long. Many of these items have vague descriptions that assume that those carrying out the work already know where things are located and how to update them, which frequently they don't. Some items may be obsolete. This results in perpetually incomplete leadership change issues, and new sig-leads missing important communications.

Example: one thing that needs to happen is that the new lead is added to the sig-X-leads mailing list, which will be located under the SIG in the k8s.io repo. However, the current checklist just has a vague reference to "mailing lists".

Rather than adding increasingly detailed instructions in the checklist, it would be better to [complete the document](https://github.com/kubernetes/community/blob/main/contributors/chairs-and-techleads/leadership-changes.md) which explained exactly what each step required and where to find it.

Creating this issue as a bookmark.

/sig Contributor-Experience
attn: @palnabarun

Start by reading contributors/chairs-and-techleads/leadership-changes.md and compare each checklist item with the current process described in the issue. Verify where SIG mailing lists and related updates are located in the k8s.io repository. Done means the document explains each current step, gives locations and instructions, and omits or resolves obsolete steps.

Written by the indexing model from the issue text.